Complex Plane Impedance Analysis Research Articles

Optimal design of broadband acoustic metasurface absorbers

The absorption of low-frequency noise has always been limited by structural thickness, but the novel physical properties of sound-absorbing metamaterials provide a solution to this problem. Based on genetic algorithm, an acoustic metasurface absorber (AMA) composed of micro-perforated plates (MPPs) and impedance matching coiled-up cavities (IMCCs) is proposed. Different from previously reported metamaterials, this structure can easily provide flexible and accurate broadband sound absorption in different target frequency bands. The theoretical model behind the algorithm is established, and two optimal structures (AMA I/AMA II) are obtained for low and mid-high frequency bands. Broadband sound absorption is realized with a thickness of only 71 mm (about 1/13 of the relevant wavelength at 369 Hz), and an average sound absorption coefficient of 0.931 is achieved in the low-frequency band of 350–1000 Hz. Furthermore, by changing the frequency band of the quasi-perfect absorber to 500–2000 Hz, the average sound absorption coefficient exceeds 0.945 with a thickness of only 55 mm (about 1/11 of the relevant wavelength at 563 Hz). The reflection coefficient in the complex plane and theoretical impedance analysis are utilized to reveal the underlying mechanism of the absorption and the acoustic characteristics of the two structures, which show excellent broadband absorption performance in the low and mid-high frequency bands. This work provides a method of arbitrarily modulating surface acoustic impedance in broadband and a reference for broadband noise control.

Electrical Conduction and Relaxation in Perovskite Oxide SrCe0.98Na0.02O3 Synthesized by Solid‐State Route

AbstractPowder of SrCe0.98Na0.02O3 is synthesized by calcination at 1000 °C for 8 h via solid‐state ceramic route. The ceramic/pellet of this compound is obtained by sintering at 1200 °C for 12 h. X‐ray diffraction (XRD) technique is used to confirm single‐phase formation. Rietveld refinement of the XRD pattern of sintered powder has confirmed orthorhombic crystal structure and space group Pnma as reported for SrCeO3. Further, the purity of the synthesized compound is ensured using Raman and Fourier transform infrared spectroscopy analysis. Scanning electron microscopic studies have reflected dense microstructure and spherical shape grains with an average size of 1.80 µm. Complex plane impedance and spectroscopic analysis are employed to study electrical conduction and relaxation mechanisms in the temperature range 300–600 °C and frequency range 20 Hz to 2 MHz. The activation energy for DC conduction (Econ) and relaxation (Erelx) is found to be the same (0.77 eV). Based on the numerical value of activation energies, conduction and relaxation mechanisms are attributed to migration of doubly ionized oxygen vacancies (VO••).

Dielectric and electrical response of hydroxyapatite – Na0.5K0.5NbO3 bioceramic composite

In recent years, the development of electrically active materials for orthopedic implant applications attracted attention owing to the fact that inherent electricity of bone mediates it's various metabolic processes. In this perspective, the present work investigates the effect of incorporation of varying amounts of piezoelectric biocompatible Na0.5K0.5NbO3 (NKN) on dielectric and electrical properties of hydroxyapatite (HA) over a wide range of temperature (30–500 °C) and frequency (1 Hz – 1 MHz). The composites HA-x NKN (x = 10–30 wt%) were synthesized by solid state ceramic method and optimally sintered at 1075 °C for 2 h. X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) patterns confirmed the formation of phase pure HA and NKN in the composite system. The dielectric response of the samples has been compared with that of the existing theoretical models. The dielectric measurement suggests that the space charge as well as dipolar polarization is the dominant polarization mechanisms. The complex plane impedance and modulus spectroscopic analyses were performed to reveal the conduction mechanism. The activation energies for grain and grain boundary resistance for HA- (10–30 wt%) NKN were 1.03, 1.464, 1.28 and 1.34, 1.56, 1.30 eV, respectively. These results suggest that ionic conduction is the dominant conduction mechanism. Hydroxyl ions and oxygen vacancies are observed to be responsible for the conduction in HA-xNKN composite system. Overall, HA- x NKN composite system can be suggested as a potential material for electro-active orthopedic implant application.

Structural analysis of Ce0.83Dy0.14Ca0.03O1.90 (CDC) and enhanced electrical conductivity of its composites with alkali carbonates for LT-SOFCs

Present work mainly deals with two important aspects of co-doped ceria based solid electrolytes. First, the occurrence of micro-strain or structural distortions in ceria lattice on doping of Dy3+ and Ca2+ at the place of Ce4+. Second, an enhancement in electrical conductivity by formation of nano-composites of Ce0.83Dy0.14Ca0.03O1.90 (CDC) and eutectic mixture of sodium and lithium carbonates [(Li0.52Na0.48)2CO3] (LNCO). CDC ceramic powder was synthesized by citrate-nitrate auto-combustion route. Nano-composites were prepared by mixing the CDC powder with LNCO using a ball mill. X-ray diffraction studies were carried out to analyze the crystal structure of CDC and to study the amorphous nature of carbonates in the nanocomposites. Thermal behavior of the nanocomposites was studied by differential scanning calorimetry (DSC). XRD data of CDC were refined by Rietveld analysis to determine the lattice parameters, atomic positions, bond lengths, bond angles, oxygen deficiency and possible micro-strain. Microstructures of the specimens were studied using scanning electron microscope. Electrical conductivity of the nanocomposites was investigated by using complex plane impedance analysis. A significant improvement in electrical conductivity was observed in nanocomposites with varying concentration of carbonates. Maximum conductivity, 1.05× 10−1 S cm−1 at 500 °C, was observed in the composite with 30 wt% (CDC/30LNCO) of carbonates content.

Synthesis & characterization of Dy and Ca Co-doped ceria based solid electrolytes for IT-SOFCs

Numerous compositions in the system, Ce1−x−yDyxCayO2−δ have been synthesized using citrate-nitrate auto-combustion route. Samples sintered at 1350 °C for 4 h have density more than 93% of the theoretical value. Single phase formation has been confirmed by X-ray diffraction in all the samples. Reitveld refinement has been carried out to confirm the cubic fluorite structure with space group Fm3¯m. Surface morphology of the sintered samples show the distinct grains and grain boundaries. Complex plane impedance analysis has been employed to separate the contribution of the grains, grain boundaries and electrode/specimen interface polarizations. A significant improvement in the electrical conductivity has been observed by partial replacement of Dy3+ with Ca2+ in Ce0.80Dy0.20O1.90 (keeping total number of oxygen vacancies fixed). Composition, Ce0.83Dy0.14Ca0.03O1.90 shows the highest conductivity, 1.45 × 10−2 S/cm at 600 °C. This value is about two orders of magnitude higher than that of singly Dy3+ doped ceria (6.01 × 10−4 S/cm) at the same temperature.

Ionic conductivity of Nd3+ and Y3+ co-doped ceria solid electrolytes for intermediate temperature solid oxide fuel cells

Nanocrystalline co-doped ceria powders having composition, Ce0.80Nd0.20-xYxO1.90 has been prepared via citrate/nitrate gel auto-combustion method. Phase identification, surface morphology and electrical measurements have been made using X-ray diffraction, scanning electron microscope and two probe complex plane impedance analysis respectively. X-ray diffraction patterns show formation of the single phase having fluorite structure similar to ceria. More than 92% of the theoretical density has been obtained after sintering at 1350 °C. AC impedance measurements have been carried out to separate the contributions of grains, grain boundaries and electrode/specimen interface to the total observed resistance in the temperature range 200–600 °C. Enhancement in the ionic conductivity has been observed due to substitution of Nd3+ and Y3+ in ceria. The composition, Ce0.80Nd0.18Y0.02O1.90 shows the maximum conductivity 1.28 × 10−2 S/cm at 600 °C. This value is about 40% higher than that reported for the composition Ce0.80Nd0.20O1.90.

Enhanced ionic conductivity in La3+ and Sr2+ co-doped ceria: carbonate nanocomposite

A series of ceria-based nanocomposites consisting of Ce0.85La0.125Sr0.025O1.9125 (LSCO) and binary carbonate mixture Li2CO3–Na2CO3 (LNCO) have been prepared as functional electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs). These have been characterized using powder X-ray diffraction, scanning electron microscope, differential thermal analysis, and measurement of conductivity as a function of temperature using complex plane impedance analysis. Crystalline ceria-based single phase formation has been found in all the composites. Carbonates are present as an amorphous phase in the composites. Impedance analysis has been used to study the electrical behavior of the composites. A jump in the conductivity vs temperature plots has been observed in all the composites containing different carbonate contents. This is related to superionic transition at the interfaces. Conductivity of the composites increases with increasing amount of carbonate. This is due to the increase in the interfacial area between the two phases, which promotes interfacial interaction between them. Composition, LSCO/35LNCO, shows conductivity of 0.203 S cm−1 at 500 °C with an activation energy of conduction of 0.19 eV.

Preparation and characterization of ceria co-doped with Ca and Mg

The aim of the present investigation was to study the effect of doping of magnesium and calcium on the ionic conductivity of CeO2 in the system Ce1−xCax−yMgyO2−x (x=0.150) for its use as a solid electrolyte in the intermediate temperature solid oxide fuel cells (IT SOFC).Attempts have been made to synthesize a few compositions in this system with x=0.150 and y=0.000, 0.050, 0.060, 0.065 and 0.070. The precursor materials have been synthesized by auto-combustion method. Solid solution forms in compositions with y≤0.060. Microstructures of thermally etched samples have been studied by scanning electron microscopy (SEM). In order to evaluate the total electrical conductivity, σt, use is made of complex plane impedance analysis. Impedance measurements were made in the frequency range 1Hz–1MHz and temperature range 250–500°C. It is found that co-doped samples show higher conductivity than undoped and singly doped samples.

Effect of strontium (Sr) doping on the conductivity of ceria

A few compositions in the system Ce 1− x Sr x O 2− x with 0.05 ≤ x ≤ 0.20 have been prepared by auto-combustion method. More than 93% of theoretical density has been achieved by sintering at 1350 °C for 4 h. Solid solution has formed in the composition with x = 0.05. All other compositions have been found to contain XRD lines of SrCeO 3 beside the major fluorite phase. Complex plane impedance analysis has clearly revealed the contribution of grains, grain boundaries, and electrode specimen interface to the total observed resistance of the sample. Conduction occurs mainly due to diffusion of O 2− ions through oxygen vacancies as indicated by values of activation energy of conduction. Composition, Ce 0.95 Sr 0.05 O 1.95 exhibits the highest ionic conductivity 3.26 × 10 −3 S cm −1 at 500 °C among the series. Ionic conductivity decreases gradually with increasing x. This is due to the formation of a second phase SrCeO 3 and increasing probability of formation of neutral associated defect pairs, S r ′ ′ Ce − V O .

Structural studies of NASICON material of different compositions by sol–gel method

The NASICON (Na 1 + x Zr 2Si x P 3 − x O 12) is a well known solid electrolyte material with high ionic conductivity. The ion conductivity can be improved by modifying the structure. The NASICON powders with different compositions (by varying x) have been prepared by sol–gel method. The structural and conductivity measurements have been done by XRD, complex plane impedance analysis and electrochemical cell method. The results indicate that the ac conductivity and Na + ion selectivity are higher for x = 2.05 as compared to other compositions. The enhancement of Na + ion conductivity for x = 2.05 has been attributed to modifications in the orientations of tetrahedral structures which lead to change in the bottleneck size. The results have been confirmed by X-ray diffraction (XRD).

Electrical conductivity of undoped, singly doped, and co-doped ceria

In order to investigate the effect of single doping and co-doping on the enhancement of ionic conductivity in ceria (CeO2), CeO2 and a few compositions in the system Ce0.85Sm0.15 − xGdxO1.925 (x = 0.00, 0.06, 0.09, and 0.15) were prepared using citrate–nitrate auto-combustion method. Gels were characterized by simultaneous differential thermal analysis and thermogravimetric analysis to confirm the formation of end product from the precursor. All the compositions were found to be single-phase solid solution from their X-ray diffraction pattern. Complex plane impedance analysis clearly revealed the contribution of grains, grain boundaries, and electrode specimen interface to the total value of the resistance. The value of activation energy, Ea, of conduction shows that the conduction process is mainly due to diffusion of O2− ions through oxygen vacancies. Effect of doping has been analyzed using the concept of radius mismatch and effective index reported earlier in the literature.

Dielectric properties of iron doped calcium copper titanate, CaCu 2.9Fe 0.1Ti 4O 12

CaCu 2.9Fe 0.1Ti 4O 12 (CCFTO) has been prepared by a novel semi-wet route and its dielectric properties have been studied in the temperature range 300–500 K. It is found that dielectric constant ( ɛ) decreases drastically in the frequency range 100 Hz to 1 MHz. Complex plane impedance and modulus analysis was done to understand this drastic decrease in ɛ. Oxidation state of various ions was studied using X-ray photoelectron spectroscopy (XPS). The decrease in the permittivity of CCFTO can be attributed to two factors: the suppression of the Ca/Cu disorder in CCFTO which is observed in CaCu 3Ti 4O 12 (CCTO) and the absence of the grain boundary internal barrier layer capacitance mechanism.

Dielectric properties of iron doped calcium copper titanate, CaCu3Ti3.9Fe0.1O12 ceramic

Dielectric properties of iron doped CaCu3Ti4O12 (CCTO), viz. CaCu3Ti3.9Fe0.1O12 (CCTFO) prepared by a novel semi-wet route have been investigated. X-ray diffraction of powder sintered at 900 °C show formation of single phase solid solution. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of CuO rich phase at grain boundaries of CCTFO. Nature of dielectric relaxation observed above room temperature is studied using complex plane impedance analysis and modulus spectroscopy. It has been found that out of the two relaxations reported earlier above room temperature, one occurring at lower temperature is due to grainboundaries interfacial polarization.

Oxide ion conductivity and relaxation in CaREZrNbO 7 (RE = La, Nd, Sm, Gd, and Y) system

CaREZrNbO 7 (RE = La, Nd, Sm, Gd and Y) system changed from fluorite (F)-type to pyrochlore (P)-type structure when the ionic radius ratios, r(Ca 2+–RE 3+) av/ r(Zr 4+–Nb 5+) av were larger than 1.34. Thus, the La, Nd, and Sm compounds have a cubic P-type structure and the Gd and Y ones have a defect F-type structure. The electrical conductivity was measured using complex-plane impedance analysis over a wide temperature (300–750 °C) and frequency (1 Hz–1 MHz) ranges. The conductivity relaxation phenomenon was observed in these compounds and the relaxation frequencies were found to show Arrhenius-type behavior and activation energies were in good agreement with those obtained from high temperature conductivity plots. These results support the idea that the relaxation process and the conductivity have the same origin. The ionic conductivity of CaREZrNbO 7 (RE = La, Nd, Sm, Gd and Y) system showed the maximum at the phase boundary between the F-type and P-type phases. On the other hand, the activation energy for the conduction decreased in the F-type phase and increased in the P-type phase with increasing ionic radius ratio. Among the prepared compounds, CaGdZrNbO 7 showed the highest ionic conductivity of 9.47 × 10 − 3 S/cm at 750 °C which was about twice as high as that observed in Gd 2Zr 2O 7 (4.2 × 10 − 3 S/cm at 800 °C). The grain morphology observation by scanning electron microscope (SEM) showed well-sintered grains. AC impedance measurements in various atmospheres further indicated that they are predominantly oxide ion conductors at elevated temperatures (> 700 °C).

The development of a ‘labeless’ immunosensor for the detection of Listeria monocytogenes cell surface protein, Internalin B

Electrochemical impedance spectroscopy (EIS) is a widely used technique for probing bioaffinity interactions at the surfaces of electrically conducting polymers. EIS methods can be employed to investigate ‘labeless’ detection of analytes via impedimetric transduction. This paper describes the development of a direct immunosensor for the detection of a cell-surface protein on Listeria monocytogenes, an extremely important food-borne pathogen. L. monocytogenes are facultative anaerobic, non-sporing, Gram-positive, motile rods that employ the surface bound protein, Internalin B (InlB), to promote invasion into host cells. A recombinant form of InlB was previously cloned and expressed in Escherichia coli and a panel of antibodies and antibody fragments directed against the protein were also produced. Here, we describe how a portion of the recombinant InlB protein, the F3 fragment, and an anti-InlB polyclonal antibody, were used to develop a platform for the labeless immunosensing of InlB. Sensors were fabricated by electropolymerisation of planar screen-printed carbon electrodes with polyaniline (PANI), to produce a conductive substrate. Polyclonal anti-InlB antibody was subsequently incorporated onto the PANI layer using a biotin–avidin system for site-specific immobilisation. The sensors were then probed with varying concentrations of InlB antigen and the impedimetric response at each concentration was recorded. An anti-IgG antibody was immobilised at the electrode surface, as a control and subsequently exposed to the same concentrations of InlB. Impedimetric data for the control sensors were also recorded. Upon exposure to a range of concentrations of antigen, complex plane impedance analyses were used to relate the differing redox states of the polymer layer, to the possible charge transfer at the surface, with respect to the related mechanisms between the antibody and the polymer. These effects were subsequently monitored to assess the impedance of the polymer thereby determining the amount of bound antigen at the sensor surface. Calibration profiles for both sample (InlB) and control (IgG) sensors were constructed. A limit of detection of 4.1 pg/ml was achieved for Internalin B.

Barrier Layers Formation in Tin Substituted Calcium Copper Titanate CaCu3Ti4-xSnxO12 (0≤x≤1.0)

A few compositions in the system CaCu 3 Ti 4- x Sn x O 3 (0≤ x ≤1.0) were synthesized by solid state diffusion controlled thermochemical process. Powder X-ray diffraction patterns of all the compositions show that these compositions are single phase solid solution. All the samples have cubic crystal structure similar to undoped CaCu 3 Ti 4 O 12 . Microstructure shows that average grain size is about 10 µm. Dielectric measurements have been carried out in the temperature and frequency range 300–450 K and 1 kHz–1 MHz, respectively. It has been shown by complex plane impedance and modulus analysis that barrier layers form at grain boundaries in these materials. These barriers impart high value of dielectric constant to the resultant ceramic. Dielectric constant, e r can be enhanced and dielectric loss (loss tangent), D can be reduced further by chemical infiltration.

Synthesis, structure and electrical behaviour of nickel-doped barium stannate

The possibility of formation of a solid solution in the system BaSn 1− x Ni x O 3 has been explored up to x ≤ 0.20. It has been confirmed that single phase solid solution forms up to x ≤ 0.10. Dielectric and ac conductivity of the samples have been studied in the temperature range 350–650 K and frequency range 10 Hz–2 MHz and dc conductivity of the samples have been measured in the temperature range 550–1100 K. Seebeck coefficient ‘ α’ of the samples have been measured in the temperature range 350–650 K. Negative value of ‘ α’ in the entire range of temperature measurement shows that conducting species are negatively charged. On the basis of value of activation energy for dc conduction and sign of Seebeck coefficient, conduction in the low temperature region (below 500 K) is attributed to hopping of weakly bonded electrons among Sn 2+ ⇔ Sn 4+ or Sn 3+ ⇔ Sn 4+ sites and that in the high temperature region (above 500 K) to hopping of doubly ionized oxygen vacancies (V o ). Complex plane impedance analysis have been made to understand the conduction behaviour of grain and grain boundaries separately.

Electric conductions in La 0.9Sr 0.1GaO 3− δ and La 0.9Sr 0.1Ga 0.9Mg 0.1O 3− δ

Electric conductions in La 0.9Sr 0.1Ga 1− x Mg x O 3− δ (LSGM; x=0 and 0.1) have been elucidated by ac and dc methods as a function of temperature. Using complex-plane impedance analyses and dielectric relaxation processes along with dc results, activation energy for electric conduction, migration energy of O 2− ions ( E M), and energy required to create a free mobile oxygen vacancy which assists O 2− migration ( E O) within intragrains and in boundaries have been obtained separately. Dielectric dispersion due to a distribution of relaxation times in boundaries is observed. The activation energy for each electric conduction is nearly equal to sum of E M and E O. Lattice distortion due to a large difference in ionic radii of Mg 2+ and Ga 3+ brings about high migration energy within intragrains in x=0.1 specimen compared with that of x=0. Such high migration energy has an adverse effect on improvement of ionic conductivities but excess oxygen vacancies compensate this adverse effect. In boundaries, disturbances in coulombic potential fields due to disordered ionic arrangements discourage ionic conductions.

Synthesis, structure and electrical behaviour of lanthanum-doped barium stannate

A few samples in the system Ba1−xLaxSnO3 (up to x ⩽ 0.15) have been synthesized via the solid state ceramic route. Powder x-ray diffraction pattern of the samples confirm the formation of a single phase solid solution only in the samples with x up to ⩽0.05. It was found that single phase compositions have a cubic crystal structure similar to that of undoped barium stannate. The ac electrical and dielectric properties of single phase samples have been studied in the frequency range 10 Hz–5 MHz for temperatures ranging from 300 to 550 K. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents 300–420 K, and region II, which governs 420–550 K. Conduction and dielectric relaxation in both temperature regions are explained in terms of variable range hopping of electrons. Complex plane impedance analysis revealed that the specific conductivity of the grains is two orders of magnitude higher than that of the grain boundaries.

Relation of conduction changes and magnetic properties inNd1−xPbxMnO3 (0.10 ≤ x ≤ 0.25)

Measurements of bulk conductivity and dielectric relaxation processes by ac methodsincluding complex-plane impedance analyses have been carried out on insulating, together with measurements of four-probe dc conductivity and magnetic susceptibility, so asto investigate the correlation between bulk conduction and short-range ferromagnetism due todouble-exchange (DE) interactions working even above ferromagnetic ordering temperature(Tc). In bulk conduction, there are three temperature regimes where different processesdominate the electronic conduction: (i) the paramagnetic regime above thetemperature at the onset of deviation of inverse magnetic susceptibility from theCurie–Weiss law, (ii) the intermediate regime and (iii) the temperature region belowTc. Though the polaronic conduction occurs in both high-temperature andintermediate regions, the hopping energy and the energy required to createa free hopping polaron differ considerably in these regimes. An anomalyemerges in both bulk conduction and dielectric relaxation processes aroundTc atx = 0.20 and this anomalybecomes more clear at x = 0.25. By taking account of electron–phonon interactions, these results are discussed mainlyin terms of the DE mechanism that brings about short-range ferromagnetism.